London’s Red Double-Deckers Go Greener

28 April 2006

The Enviro400 double-decker.

Transport for London (TfL) is putting into service 39 new double-decker diesel buses built by Alexander Dennis that are almost 20% more fuel efficient than their predecessors and that meet Euro-4 standards of emissions.

The new Enviro400-model buses, which will be put into operation over the next three months, also generate 18% less carbon dioxide and reduce emissions of oxides of nitrogen by more than 46%.

A new High-Pressure Common-Rail fuel system on the engine can deliver up to 1600 bar injection pressures. Injection pressure can be virtually constant at all speeds, realizing greater flexibility and precision in controlling both injection rates and timing.

The new High-Pressure Common-Rail fuel system is fully integrated with Cummins high-precision electronic management system, driven by an upgraded ECM (Electronic Control Module) with a processing speed over twice as fast as the previous ECM. The ISBe engine management system continually maintains an optimum balance between load demands, fuel-efficiency and emissions control.

More than 60% of the current London bus fleet meets Euro-3 emissions standards with the remainder achieving Euro-2 standards.

All Euro-2 and Euro-3 buses have been fitted with particulate filters, which reduce emissions of fine particles, carbon monoxide and hydrocarbons from the vehicle exhaust by more than 90%.

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Comments

The people who tout these "green" buses NEVER indicate the expected fuel economy of these vehicles. The old, politically-incorrect double-decker Routemasters would achieve 12 Miles to the Imperial Gallon (that's about 10 m.p.g., U.S.) using a 130 H.P., 680 c.i.d. Leyland diesel engine. I would doubt that the new buses come anywhere close to the economy achieved by those old high torque, low horsepower engines, especially if they use a Cummins diesel.

Considering the fact that these diesel engines will be operating almost exclusively in highly built up and densely populated areas (unlike diesels on most railroads or freight trucks), it is entirely reasonable to strictly limit health-critical emissions, even at the expense of fuel economy and greenhouse gas emissions.

Unmitigated diesel exhaust can be incredibly dirty and dangerious (sulfur compounds, NOx compounds, PM emissions), and the public health effects of spewing that sort of garbage out of an urban bus fleet can be substantial. In this case especially, our goals can reasonably be to prevent smog, asthma and cancer first, and worry about greenhouse gas second. There are other places where we can now focus our efforts to get CO2 efficiences, without undue risk of harm.

Over the coming five-year horizon (when I'm sure the old Euro-2 buses will be retired), we can talk about getting GM/Allison hybrid drivetrains and biodiesel compatible fuel systems to tackle the global warming aspect of urban bus fleets. By keeping private cars off the road, they already do plenty to curb global warming, and by what I've seen of public transit cost structures, fuel is not the biggest ticket item on their budget sheets (labor, capital costs and even upkeep tend to be).

Trading fuel economy for public health is a known part of the clean-diesel equation, and a tradeoff usually worth making. These new buses are "green" in that respect, or at least not soot-colored. The old "politically incorrect" buses are also just that: Politically incorrect, in the sense that the electorate would not be pleased to learn that the city transit authorities are continuing to kill them at higher rates despite the availability of cleaner technologies.

Considering the fact that these diesel engines will be operating almost exclusively in highly built up and densely populated areas (unlike diesels on most railroads or freight trucks), it is entirely reasonable to strictly limit health-critical emissions, even at the expense of fuel economy and greenhouse gas emissions.

Unmitigated diesel exhaust can be incredibly dirty and dangerious (sulfur compounds, NOx compounds, PM emissions), and the public health effects of spewing that sort of garbage out of an urban bus fleet can be substantial. In this case especially, our goals can reasonably be to prevent smog, asthma and cancer first, and worry about greenhouse gas second. There are other places where we can now focus our efforts to get CO2 efficiences, without undue risk of harm.

Over the coming five-year horizon (when I'm sure the old Euro-2 buses will be retired), we can talk about getting GM/Allison hybrid drivetrains and biodiesel compatible fuel systems to tackle the global warming aspect of urban bus fleets. By keeping private cars off the road, they already do plenty to curb global warming, and by what I've seen of public transit cost structures, fuel is not the biggest ticket item on their budget sheets (labor, capital costs and even upkeep tend to be).

Trading fuel economy for public health is a known part of the clean-diesel equation, and a tradeoff usually worth making. These new buses are "green" in that respect, or at least not soot-colored. The old "politically incorrect" buses are also just that: Politically incorrect, in the sense that the electorate would not be pleased to learn that the city transit authorities are continuing to kill them at higher rates despite the availability of cleaner technologies.

The Leyland 680 diesels put out about 130 H.P. at 2000 r.p.m. with approximately 340 lb-ft. of torque.

This engine can essentially do the same amount of work as a thirsty Cummins which has to generate work at a rate of 350 H.P. to produce the same amount of torque.

An engine producing 350 H.P. burns fuel about 2.69 times quicker than those old prehistoric Leylands for the same work; in other words, the newer Cummins only gets about 40% of the fuel economy as the Leyland.
This is simple high-school physics.

This thus puts these new "gee-whiz" buses at about 4 m.p.g., which is sadly typical of most modern buses.

"Save the planet, kill yourself"????

I suppose just because I point out a fact that challenges some pre-conceived notion that you have stored somewhere in your brain, you suggest that I kill myself? This is a good example of a moronic, silly-ass comment. Please just tell me how a vehicle that burns 2.5 gallons of diesel to go 10 miles compared to one that uses only 1 gallon to move 10 miles is more environmentally friendly?

But thanks anyhow for the specs for the Cummins Diesel. With that, I was able to answer my own question concerning the fuel economy of these "green" buses!

Dave Zeller:
I'm not even going to try correcting your post. Most of your statements are just plain incorrect.

"This engine can essentially do the same amount of work as a thirsty Cummins which has to generate work at a rate of 350 H.P. to produce the same amount of torque."

What are you talking about? You clearly do not understand the difference between HP and torque.

"An engine producing 350 H.P. burns fuel about 2.69 times quicker than those old prehistoric Leylands for the same work; in other words, the newer Cummins only gets about 40% of the fuel economy as the Leyland.
This is simple high-school physics."
WHAT!?!? No its not! You are using peak HP to calculate fuel consumption at part throttle operation. Are you for real?

"This thus puts these new "gee-whiz" buses at about 4 m.p.g., which is sadly typical of most modern buses."
You obviously didn't read the first sentance of the article where it clearly states that the new buses are "20% more fuel efficient than their predecessors."

I'm not going to dispute any fuel consumption claims, or emission statements but I wonder... if there is 350HP available then it will be used, right? Common law of humanity I guess, when it's there we use it and keep doing so until we run out of it.
The Leyland 680 did the job with 150Hp, so why do we need 350Hp now? The Cummins might be better on emission but would have been a lot better if it wasn't churning out 350Hp! So don't call it Green.

Of course you could say that you need 350Hp... but do you? You see I have a Leyland with a 680 in it. It is converted into a motorhome, cruises easily at 90 (which will be hard to do in London anyway, and also pulls a 3,5 tonne trailer while doing it. Don't need 350 horses for that; 150 Leyland Cydesdales will do it. Fuel consumption? About 4-4.3 km/litre including trailer (and this is not some controlled manufacturers figure but real life experience).

There are a couple of things missing in the Green debate however. Like I said when there is 350Hp available it will be used, so there is a significantly higher amount of tyre wear. Tyres that have to be produced, transported and 'recycled'. How much pollution is in that? Hard to calculate, you bet it is but you don't have to be a rocket scientist to realise that it'll be difficult to offset that to a claimed 20% fuel efficiency.

And how much emission is created in producing and transporting these new busses anyway? Perhaps it would have been better to 'recycle' the old ones...

What can we expect of the reliability? Maybe not of much interest in London, but here in Australia where distances are vast, conditions are extreme and engines are used... Leylands 680 has one hell of a reputation for being economical and ultra reliable. We use Cummins in Road Trains pulling 4 trailers and 170 tonnes in weight... we laugh our heads off when we hear about Europeans needing 350 horses to pull Dinky Toys.